1. Field of the Invention
The present invention relates to a liquid crystal optical device using a ferroelectric liquid crystal.
2. Description of the Related Art
A liquid crystal optical device (hereinafter referred to as "FLC.LCD") using a ferroelectric liquid crystal was proposed by N. A. Clark and S. T. Lagerwall, etc., and is disclosed in U.S. Pat. Nos. 4,367,924, 4,563,059, 4,813,767, and 4,840,463. In this FLC.LCD, a pair of transparent substrates are disposed to oppose to each other, and aligning films are respectively formed on the opposed surfaces thereof. A liquid crystal material (hereinafter referred to as "a ferroelectric liquid crystal") exhibiting Chiral Smectic C* phase is sealed between the pair of transparent substrates. The aligning films function to align the liquid crystal molecules of the ferroelectric liquid crystal in one direction. By setting the gap between a pair of transparent substrates to the extent of the spiral pitch (e.g., approx. 2.5 .mu.m or less) of a liquid crystal material exhibiting Chiral Smectic C* phase the spiral is released, thereby obtaining an uniaxial alignment having a layer surface perpendicular to the opposed surfaces of the substrates. Thus, in the FLC.LCD in which the uniaxial alignment is obtained, the alignment of the liquid crystal molecules is stable in two states, thereby obtaining tow optically stable states. That is, the FLC.LCD has a memory characteristic.
This memory characteristic depends upon the mutual action between the liquid crystal molecules and the surfaces of the aligning films. For example, if the surface energies of the aligning films are large with the result that the mutual action with the liquid crystal molecules is large, alignment restrictive force for arranging the liquid crystal molecules in a predetermined one direction is increased to easily obtain the uniaxial alignment. Since the aligning state is stable, memory characteristic is high.
However, since the alignment stability becomes high when the alignment restrictive force of the aligning film is large it becomes difficult to vary the aligning state. Therefore, it becomes difficult to alter one stable alignment state to the other stable aligning state by applying an electric field, and the responding characteristic of the liquid crystal by the application of the electric field is deteriorated.
The conventional FLC.LCD employed an obliquely deposited layer of silicon oxide (SiO) as an aligning film, and did not practically reduce the operating characteristic of the liquid crystal but could not obtain a completely uniform alignment. Accordingly, the FLC.LCD could not obtain sufficiently high stability of the alignment. Thus, the conventional FLC.LCD could not obtain practically sufficient bistability, sufficient memory characteristic.
In the conventional FLC.LCD, the thickness of the liquid crystal layer is extremely thin such as approx 2.5 .mu.m or less, and only an alignment dielectric layer is interposed between transparent electrodes formed on the opposed surfaces of a pair of substrates and the liquid crystal layer. Accordingly, when fine electroconductive foreign material is mixed in the liquid crystal layer, a short-circuit occurs between the electrodes of a pair of the substrates.
It is an object of the present invention to provide a liquid crystal optical device using a ferroelectric liquid crystal, which does not practically lower operating characteristics of a liquid crystal by an electric field but can provide sufficient memory characteristic in practice and positively prevent a short-circuit between a pair of electrodes of a substrate even if a conductive foreign material is mixed in a liquid crystal layer.